Tuberculosis: A Global Overview of the Situation Today (PDF)

Update Le point Tuberculosis: a global overview of the situation today* P. Sudre,' G. ten Dam,2 & A. Kochi3 The overall tuberculosis situation in the world in 1990 and its recent trends are reviewed by an analysis of the case notifications to WHO and tuberculosis mortality reports. Estimates of th...

Update Le point Tuberculosis: a global overview of the situation today* P. Sudre,' G. ten Dam,2 & A. Kochi3 The overall tuberculosis situation in the world in 1990 and its recent trends are reviewed by an analysis of the case notifications to WHO and tuberculosis mortality reports. Estimates of the prevalence of tuberculosis infection and the incidence of tuberculosis disease and deaths predicted in 1990 were car- ried out with simple epidemiological models. Approximately one third of the world's population is infected with Mycobacterium tuberculosis. In the past decade, an average of 2.5 to 3.2 million cases were notified every year globally, the small de- crease in notification rates in recent years being offset by population growth. In 1990, an estimated 8 million people developed tuberculosis worldwide and 2.6 to 2.9 million died. The majority of these cases and deaths occurred in Asia, with an increasing number among HIV-infected individuals, especially in Africa where an upward trend is clearly detectable. Data on tuberculosis cases notified by WHO Member States demonstrate the magnitude of the problem but must be interpreted with caution. Being less than the expected incidence, they reflect the inadequacies of tuberculosis control programmes. This review confirms the very high global magnitude of the tuberculosis problem and calls for an urgent revitalization of tuberculosis control programmes throughout the world. Introduction The present update describes the overall global situation of tuberculosis in 1990 and its trends since Tuberculosis, long known to be a major cause of 1974. Several epidemiological indicators are used to morbidity and mortality throughout the world, has describe both magnitude and trends; the most impor- for the past several decades been a neglected disease tant are the prevalence of infection, notification in both industrialized and developing countries. rates, the predicted incidence of disease, and mortali- However, it is now attracting renewed interest, and ty from tuberculosis. Information about these indica- significant efforts to revive control activities are cur- tors was obtained through official notifications of rently under way (1). This is occurring largely cases and deaths, and projections made using simple because of the increased incidence of tuberculosis in epidemiological models. many HIV-epidemic countries (2, 3), the availability and proven effectiveness of short-course chemo- therapy (4), and the realization that tuberculosis con- trol is one of the most cost-effective health interven- Methods and data sources tions in developing countries (5). Annual risk of infection and prevalence of * From the Tuberculosis Unit, Division of Communicable infection Diseases, World Health Organization, 1211 Geneva 27, The probability for an uninfected individual to be- Switzerland. Requests for reprints should be sent to this come infected in a one-year period (annual risk of address. A French translation of this article will appear in a later issue of the Bulletin. infection) is the most informative epidemiological ' Medical Epidemiologist, Tuberculosis Unit. indicator (6). It is used to predict the number of new 2 Scientist, Tuberculosis Unit. cases of tuberculosis that can be expected in high- 3Chief, Tuberculosis Unit. prevalence countries (7, 8). The annual risk of infec- Reprint No. 5260 tion was calculated from tuberculin survey data, Bulletin of the World Health Organization, 70 (2): 149-159 (1992) © World Health Organization 1992 149 P. Sudre et al. available since 1975,a using the age-specific preva- the observations that (1) in high prevalence coun- lence of infection. A model that takes into considera- tries, there are 39 to 59 cases of smear-positive pul- tion the annual risk of infection, i.e., the rate of monary tuberculosis per 100 000 population for every change of the annual risk of infection in the past, 1% annual risk of infection, and (2) there are an and the age distribution of the population was used additional 1.22 cases of smear-negative and extrapul- to determine region- and age-specific prevalences of monary tuberculosis for each case of smear-positive tuberculosis infection. The prevalence of dual tuber- tuberculosis (8). The number of cases of tuberculosis culosis/HIV infection was estimated by applying expected in each country was calculated using an the prevalence of tuberculosis infection in the 15- annual risk of infection of 1.5% to 2.5% for the coun- 49-year age group to populations which are thought tries of the African Region, 0.5% to 1.5% for coun- to be infected with HIV in this age group.b tries in Central and South America and the Eastern Mediterranean Region, and 1% to 2.25% for coun- tries in the South-East Asian and Western Pacific Case notifications Regions (8). The additional number of HIV-related The Expanded Programme on Immunization (EPI) tuberculosis cases was obtained by applying a 10% has been routinely collecting information on tubercu- annual breakdown rate to the number of dually losis morbidity since 1974. Official reports from infected individuals (10). countries or from WHO Regional Offices are com- piled, updated and published twice a year. In this Coverage analysis, outliers (defined as numbers of cases noti- fied in one year that are more than three times, or Coverage (also called case detection ratio) represents less than one third, of those notified in the previous the fraction of all individuals with active tuberculosis and the following year) were removed in order to in- who have been diagnosed, treated and reported. For crease the consistency of reporting within a country. practical purposes, it is approximated by the ratio of This was justified because such large year-to-year reported cases to expected cases, expressed as a per- variations are likely to be due to programmatic centage.d changes rather than to changes in the epidemiology The highest, the average, and the lowest num- of tuberculosis. Denominators were obtained from bers of notifications expected in 1990 were obtained World Bank projections (9) and were provided by for each country by applying the 1980-89 highest, EPI for small countries.c average and lowest notification rates to the 1990 The 10-year average and the highest number of population. These numbers were then compared with tuberculosis cases notified annually between 1980 the numbers of cases predicted in 1990 to make esti- and 1989 were obtained for each country. Secular mates of the range of coverages. trends were determined using the 5-year annual means or the highest numbers of cases reported Mortality annually in these intervals. To compile regional figures, cases reported in all countries of each region Tuberculosis mortality is due to failure or delay in were totalled and the regional notification rate was diagnosing the disease or to ineffective treatment calculated using the population of the region as (lack of compliance, resistant organism). Death certi- denominator (the populations of countries not report- ficates are used to determine the overall mortality ing were removed from the denominator). and the relative importance of tuberculosis deaths among all the other causes of death. Mortality figures available from 62 countries were abstracted Expected incidence from the World health statistics annual 1988 (11) The incidence of expected new cases of tuberculosis and 1990 (12). annually was calculated for each country and com- The expected tuberculosis mortality was calcula- piled for the regions. The calculation was based on ted assuming that 50% of the untreated cases predic- ted in 1990 died (8). It was also assumed that, when the cure rate is 50-60%, as currently observed in most developing countries, the fatality of notified a Cauthen, G.M. et al. Annual risk of tuberculosis infection. cases is 15% on average (8). Although case fatality Unpublished WHO document, WHO/TB/88. 154, 1988. b Current and future dimensions of the HIVIAIDS is higher in treated smear-positive tuberculosis than pandemic: a capsule summary. Unpublished WHO document, WHO/GPA/SFI/90.2.Rev 1, 1990. c Expanded Programme on Immunization. Information system. d Snider, D.E. et al. Evaluation of tuberculosis control pro- Unpublished WHO document, WHO/EPI/CEIS/90.2, 1990. grammes. Unpublished WHO document, April 1990. 150 WHO Bulletin OMS. Vol 70 1992  Global overview of tuberculosis in smear-negative patients, the same case fatality was Table 1: Worldwide prevalence of tuberculosis infec- used for smear-positive cases and smear-negative tion, 1990 cases because, in developing countries, the former Number are largely identified and therefore as likely to sur- Prevalence infected Percentage vive as the smear-negative patients (8). The propor- Region (%) (millions) of total tion of treated patients was obtained using the aver- Africaa 33.8 171 9.9 age and the high estimate of the coverage to calculate Americasb 25.9 117 6.8 a low and a high estimate of mortality. Eastern Mediterraneana 19.4 52 3.0 Two estimates of the number of HIV-related South-East Asiaa 34.3 426 24.7 tuberculosis deaths were calculated: the lower esti- Western Pacificc 43.8 195 11.3 mate assumed that the case fatality ratio and the China 33.7 379 22.0 treatment coverage were identical for HIV-infected Europea and othersd 31.6 382 22.2 and non-infected tuberculosis cases; the higher esti- All Regions 32.8 1722 100 mate was calculated assuming that the case fatality for HIV-related tuberculosis cases was 50% regard- a Includes all countries in the WHO Region. b Includes all the countries of the American Region of WHO, less of treatment. except USA and Canada. The WHO regional classification of countries c Includes all the countries of the Western Pacific Region of was used for the European, Eastern Mediterranean, WHO, except China, Japan, Australia and New Zealand. d USA, Canada, Japan, Australia and New Zealand. African and South-East Asian Regions. However, China (because no notification report was available) and Japan, Australia, New Zealand, Canada and the USA (because they are industrialized countries with a low prevalence of tuberculosis) were classified adult population (aged 15 to 49 years) are infected separately. Therefore, the American and Western with tuberculosis. Although more than 1.5 million Pacific Regions referred to in this article do not individuals were infected with HIV in Europe and exactly cover the areas as in the WHO definition. the five industrialized countries the prevalence of tuberculosis infection was relatively low among 15-49-year olds so that dual HIV/tuberculosis infec- Results tion was relatively infrequent; less than 6% of all dual HIV/tuberculosis infected people lived in these Prevalence of tuberculosis infection countries (Table 2). One third of the world's population (1700 million) is infected with Mycobacterium tuberculosis. The pre- Tuberculosis notifications valence is highest in the Western Pacific Region (44% of the population infected) and lowest in the Country reports. Out of 194 countries and states lis- Eastem Mediterranean Region (19%). The majority ted in the EPI file, 8 (4%) have not reported tubercu- of infected individuals live in the South-East Asian losis cases at all since 1974: 3 out of 46 (6%) in the Region (25%), China (22%), and in Europe and the African Region of WHO (Comoros, Namibia, St five industrialized countries mentioned above (22%) Helena), 1 out of 47 (2%) in the Region of the (Table 1). Americas (Netherlands Antilles), 1 out of 11 (9%) The age distributions of tuberculosis infection in in the South-East Asian Region (Democratic Peoples sub-Saharan Africa and Western Europe are presen- Republic of Korea), 1 out of 34 (3%) in the Westem ted in Fig. 1 and 2. Although the overall prevalences Pacific Region (China), and 2 out of 32 in the of infection are similar in both parts of the world European Region (Albania and San Marino). (28% in Western Europe and 34% in sub-Saharan Notifications. The mean number of tuberculosis Africa), the majority of infected individuals in Eu- cases reported annually and the highest number of rope are 50 years or older (80%) and in Africa are cases reported in one single year between 1980 and less than 50 years old (77%). In the African, South- 1989 are presented, by region, in Table 3. On av- East Asian and Western Pacific Regions, more than erage, about 2.5 million cases of tuberculosis have 50% of the adult population aged 2 15 years are in- been reported each year in the past decade: 40% oc- fected (54%, 52% and 62% respectively). curred in South-East Asia and the rest almost equally In 1990, more than 3 million individuals world- distributed in the other five Regions (8% to 14%). wide were dually infected with tuberculosis and Case notification rates were lowest in industrialized HIV. The vast majority (78%) lived in Africa countries and close to 50 per 100 000 in Africa and (2 375 000) because the prevalence there of HIV Latin America. The highest annual rate, however, infection is the highest and an estimated 48% of the was still relatively low in the latter (56 per 100 000), WHO Bulletin OMS. Vol 70 1992 151 P. Sudre et al. Fig. 1. Prevalence of tuberculosis infection, by age, in tropical and southern Africa, 1990. Prevalence (%) 20r Infected Non-infected 15 10 5 0 0-4 -9 -14 -19 -24 -29 -34 -39 -44 -49 -54 -59 -64 -69 -74 >74 Age group (years) Fig. 2. Prevalence of tuberculosis infection, by age, in Western Europe, 1990. Prevalence (%) 20 Infected 15 _ FW Non-infected 10H 5 0 0-4 -9 -14 -19 -24 -29 -34 -39 -44 -49 -54 -59 -64 -69 -74 s74 Age group (years) 152 WHO Bulletin OMS. Vol 70 1992  Global overview of tuberculosis Table 2: Worldwide prevalence of tuberculosis and HIV infection in 15-49-year-olds, 1990 HIV Prevalence of HIV/TB infected infected TB infection HIV/TB_infected Region (xl 000) (%) No. (xl000) % Africa8 5000 48 2375 77.8 Americasb 1000 30 301 9.9 Eastern Mediterraneana 30 23 7 0.2 South-East Asia,a Western Pacificc and China 500 40 200 6.6 Europea and othersd 1500 11 170 5.6 All Regions 8030 34 3053 100.0 a Includes all countries in the WHO Region. b Includes all the countries of the American Region of WHO, except USA and Canada. c Includes all the countries of the Western Pacific Region of WHO, except China, Japan, Australia and New Zealand. d USA, Canada, Japan, Australia and New Zealand. an indication of the limited variability of the data, a consistent decrease in the past 15 years and the whereas it was much higher in Africa (70 per increase in the number of cases reported in 1985-89 100 000). originated in the USSR, which began reporting to WHO in 1988. Comparison of the figures from the Trends in tuberculosis notifications. Trends were late 1970s with those for 1985-89 show that tubercu- compared by using the mean and the highest num- losis notifications (1) decreased both in absolute bers of cases reported for any one year in each of the number and in rate per 100 000 in the Eastern three periods 1974-79, 1980-84 and 1985-89. Mediterranean Region and in Europe and the five Results are presented in Table 4 for the mean num- industrialized countries, (2) increased both in ab- bers of cases. Overall, there was an increase in solute number and in rate per 100 000 in Africa 1980-84, compared with the previous period, from 2 and South-East Asia, and (3) decreased in rate per million cases (reported from 178 countries) to 2.4 100 000 in Central and South America and in million cases (from 180 countries) and a decrease in the Western Pacific Region, as well as globally, the following 5-year interval to 2.2 million cases while the actual number of cases increased, an indi- (from 164 countries). The same trend was observed cation that population growth exceeded the decrease in almost all regions when rates per 100 000 popula- in case notification rate (Table 4). Over the 15-year tion rather than cases were compared. In Europe and time span, case notification rates decreased in 101 the five industrialized countries, however, there was countries and increased in 59 (1.7:1). When the Euro- Table 3: Mean and highest number of tuberculosis cases reported annually in the world, 1980-89 Mean Highest Rate per Rate per Region Cases 100 000 Cases 100 000 Africaa 234 862 52 317 840 70 Americasb 200 608 50 225 816 56 Eastern Mediterraneana 361 720 110 602 875 183 South-East Asiaa 974 869 85 1 223 173 106 Western Pacificc 334 206 169 432 847 219 Europea 288 469 35 336 300 41 Othersd 90 084 22 105 877 26 All Regions 2 484 818 52 3 244 728 69 a Includes all countries in the WHO Region. b Includes all the countries of the American Region of WHO, except USA and Canada. c Includes all the countries of the Western Pacific Region of WHO, except China, Japan, Australia and New Zealand. d USA, Canada, Japan, Australia and New Zealand. WHO Bulletin OMS. Vol 70 1992 153 P. Sudre et al. - d a a G- _ )l- 0_ CD CDc_o0- 00 ° o. 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Vol 70 1992  Global overview of tuberculosis pean and five industrialized countries were removed Table 5: Cases of tuberculosis expected in the world in from this comparison, the ratio decrease/increase 1 99oa was 1.2:1 during the same period. This may be an in- Rate per dication of the absence of any significant improve- 100 000 Percentage ment in the tuberculosis situation in the past 15 years. Region Cases population of all cases Africab 1 160 000 220 15 Impact of HIV on notification rates. In Africa, 13 Americasc 534 000 120 7 countries for which the prevalence of HIV infection Eastern Mediterraneanb 594 000 155 7 is known to be high (Burundi, Congo, COte d'Ivoire, South-East Asiab 2 470 000 194 31 Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Western Pacificd 420 000 191 5 United Republic of Tanzania, Uganda, Zaire, China 2 127 000 191 27 Zambia, Zimbabwe) (P. Eriki, personal communica- Europea and otherse 392 000 31 5 tion, 1990) were compared with the other countries HlV-relatedf 305 000 6 4 of the Region. Reports were updated using the All Regions 8 002 000 152 100 results of a WHO questionnaire survey in 1989 and the data from programmes assisted by the a Calculated using an annual risk of infection of 1.5-2.5% in Africa, 0.5-1.5% in the Americas and the Eastern International Union against Tuberculosis and Lung Mediterranean, and 1-2.25% in South-East Asia and Western Disease (IUATLD). In the past 15 years, while the Pacific Regions. b Includes all countries in the WHO Region. average rate of reported tuberculosis cases decreased c Includes all the countries of the American Region of WHO, in the non-HIV-epidemic countries from 60 to 59 to except USA and Canada. 47 cases per 100 000 in the 1974-79, 1980-84 and d Includes all the countries of the Western Pacific Region of 1985-89 time periods, respectively, it increased from WHO, except China, Japan, Australia and New Zealand. 51 to 56 to 64 per 100 000 in the same periods in the e USA, Canada, Japan, Australia and New Zealand. f The distribution of HIV-related tuberculosis cases by region is HIV-epidemic countries. as follows: 238 000 cases in Africa (78%); 30 000 cases in Latin America (10%); 17000 cases in Europe and the five industrial- ized countries (6%); 693 cases in Eastern Mediterranean (0.2%); Incidence of tuberculosis and 20 000 cases in South-East Asia and the Western Pacific Regions (6%). Expected incidence. The regional distribution of the 8 million cases of tuberculosis estimated to have occurred in the world in 1990 is presented in Table 5. The largest numbers occurred in the South-East Coverage Asian Region (2 470 000, 31 %), China (2 127 000, 27%), and the African Region (1 160 000, 15%). The estimated 1990 coverage was 46% worldwide, According to these estimates, the annual incidence ranging from 32% to 61% when the lowest and the was highest in the African Region (220 cases per highest numbers of cases reported for a given year 100 000) and much lower in the American Region were compared with the number of expected cases. (120 per 100 000). Using the average 1980-89 noti- The coverage appeared to be lowest in Africa where, fication rate for Europe and the five industrialized on average, 24% of expected cases were actually countries (31 per 100 000), 392 000 cases of tubercu- reported (range, 16% to 32%), and highest in the losis were expected in 1990. Eastern Mediterranean Region at 70% (37% to 100%) and Western Pacific Region at 88% (61% to Impact of HIV on expected incidence. Prevalence 100%). Coverage was 42% (33% to 47%) in Latin information presented in Table 2 was used to esti- America and 44% (34% to 56%) in South-East Asia. mate the additional number of tuberculosis cases aris- ing among dual HIV/tuberculosis infected individuals. Mortality In 1990, 238 000 HIV-related tuberculosis cases Reported mortality. From 1984 to 1989, 77 809 tuber- may have occurred in Africa, 30 000 in Central and culosis deaths were reported to WHO from 62 South America, 20 000 in South-East Asia and countries (Table 6). Most countries in the European Western Pacific, and 17 000 in Europe and the five Region reported (27/32), but only a few in the other industrialized countries. Although, the global impact Regions: 3/46 in Africa, 22/45 in the Americas, of HIV seems limited with 305 000 additional tuber- 3/24 in the Eastern Mediterranean, 1/11 in South-East culosis cases worldwide in 1990 (4% of all tubercu- Asia, and 6/35 in the Western Pacific. In Europe (ex- losis cases), the cases represent a massive increase cluding the USSR) the average annual reported tuber- in Africa, boosting the overall incidence of tubercu- culosis mortality rate was 2.16 per 100 000; in the losis from 220 per 100 000 to 265 per 100 000 (20% USSR it was 7.70 per 100 000. A difference of the additional cases). same order of magnitude was observed between North WHO Bulletin OMS. Vol 70 1992 155 P. Sudre et al. Table 6: Annual number of tuberculosis deaths in the world reported in the World Health Statistics Annual 1988 and 1990 Year Death rate of Countries Tuberculosis deaths per 100 000 WHO Region reporta reporting reported population Africab 1984-87 3/46 26 2.18 Americas: 1984-88 22/45 24 932 3.99 Northc 1988 2/2 2 029 0.76 South/Centrald 1984-88 20/43 22 903 6.03 Eastern Mediterraneane 1987-88 3/24 1 275 2.36 South-East Asia' 1985 1/11 1 177 7.12 Western Pacific (excluding China)9 1987-89 5/34 4 137 2.76 China 1989 1/1 15 121 1.45 Europe: 1986-89 27/32 31 141 4.12 USSR 1988 1/1 21 800 7.70 Resth 1989 26/31 9 341 2.16 All Regions 62/191 77 809 2.96 a Year of report varies by country. b Mauritius, Sao Tome & Principe, and Seychelles. c USA. and Canada. d Argentina, Bahamas, Barbados, Brazil, Chile, Colombia, Costa Rica, Cuba, Ecuador, Guyana, Mexico, Jamaica, Panama, Paraguay, Peru, Puerto Rico, Saint Lucia, Trinidad & Tobago, Uruguay, and Venezuela. e Bahrain, Egypt, and Kuwait. f Sri Lanka. g Australia, New Zealand, Japan, Hong Kong, and Singapore. h Not reporting: Romania, Albania, Turkey, San Marino, and Monaco. and Latin America (0.76 and 6.03 deaths per 100 000, infection is also largest in the 15-49-year age group, respectively). the interaction between HIV and tuberculosis will Expected mortality. For 1990, the range of the esti- become an important consideration when planning mated number of tuberculosis deaths globally is from and targeting tuberculosis control programmes. 2 600 000 to 2 900 000 (49 to 55 deaths per 100 000 (2) In the industrialized countries, the prevalence of population), depending on the level of coverage used infection is very low among those less than 50 years to estimate how many cases received antituberculosis old, but is still high in the relatively large older age treatment. Although 32% of all deaths occurred in groups. This is a reflection of the high risk of infec- the South-East Asian Region (819 000 to 928 000) tion in the past. In these countries, an increasing pro- and 27% in China (688 000 to 780 000), the tubercu- portion of tuberculosis cases is likely to occur in the losis death rates were greater in the African Region elderly. A limitation of these projections is that they (91 to 100 deaths per 100 000) than anywhere else represent an average for several countries and only (Table 7). In 1990, there were an additional 120 000 consider age as a determinant of the prevalence of to 150 000 estimated deaths among HIV-infected infection. They do not take into consideration large tuberculosis cases. Most of them (83%) occurred in variations in the annual risk of infection in various Africa (100 000 to 125 000). subgroups of the population in which the true preva- lence of infection is likely to be much higher. Discussion Notifications Prevalence of infection Careful analysis of notifications can provide a good About one third of the total world population is insight into the tuberculosis situation, tuberculosis infected with M. tuberculosis and two epidemiologi- control activities, and their trends. When most of the cal pattems can be distinguished. (1) In the devel- population has access to health care services and oping countries the majority of infected individuals when case-reporting is mandatory (as in most indus- are below 50 years of age. This is because the annual trialized countries), tuberculosis notifications of risk of infection is still significantly high and be- newly diagnosed cases represent quite accurately the cause, in many instances, half of the population is incidence of tuberculosis (13). Official notifications, less than 15 years old. Since the prevalence of HIV however, are only as good as the national tuberculo- 156 WHO Bulletin OMS. Vol 70 1992  Global overview of tuberculosis Table 7: Projected tuberculosis mortality in the world in 1990 Low estimatea High estimateb Deaths per Deaths per Percentage 100 000 100 000 of all Region Deaths population Deaths population TB deaths Africac 481 000 91 531 000 100 18 Americasd 197 000 44 205 000 46 7 Eastern Mediterraneanc 137 000 36 163 000 43 5 South-East Asiac 819 000 63 928 000 72 32 Western Pacifice 99 000 45 110 000 50 4 China' 705 000 63 780 000 72 27 Europeg 33 000 3.9 33 000 3.9 1 Others9 h 6 000 1.4 6 000 1.4 0.2 HIV-related' 119 000 2.3 151 000 2.9 5 All Regions 2 596 000 49 2 907 000 55 100 a Using the "high level of coverage" for the calculation. b Using the "average level of coverage" for the calculation. c Includes all countries in the WHO Region. d Includes all the countries of the American Region of WHO, except USA and Canada. e Includes all the countries of the Western Pacific Region of WHO, except China, Japan, Australia and New Zealand. IAssumes the same annual risk of infection and the same service coverage as in South-East Asian countries. 9 Number of tuberculosis deaths reported in 1988. h USA, Canada, Japan, Australia, New Zealand. iThe distribution of HIV-related tuberculosis deaths would be as follows: Africa, 125 000 deaths (82%); Latin America, 14000 deaths (9%); Europe and five industrialized countries, 3000 deaths (2%); Eastern Mediterranean Region, 150 deaths (